I need some help troubleshooting here. I have an 89 2.5 yj that cranks, but doesn't start. When i turn the key, the fuel pump kicks on and is sending fuel to the rail and cranks, but doesn't actually start. It'll crank all day if i let it.

This tells me its not a fuel problem because i have fuel. Not an ecm problem because the fuel pump kicks on. Is this correct?

I have brand new spark plugs. I can spray starting fluid in the air box and it sounds like its going to start for 1/2 second, but then goes back to just cranking.

you may not have enough fuel pressure even though the fuel pump is pumping. Go to autozone and borrow the fuel pressure gauge, its free but you have to leave a deposit. Plug it into the shrader valve and report back here with the pressure.

It should be on the throttle body on your 89 2.5L. I think you should have 15 psi with the pump running. Your TBI should have a pressure adjustment screw on the pressure regulator which you screw inward to increase pressure and outward to decrease pressure.

The engine has maybe 3000 miles on it, but its been parked for two years because i took the body off to take care of some frame stuff. Didn't touch the engine though during that time. Right before it was parked, I drained fluids. Before i tried starting it, i put brand new fluids in it and new copper plugs. I haven't replaced wires though. Should i throw the old plugs back in it to see if it'll fire?

The new plugs should be ok, but you should still check to see if the gap is the same as the old ones. I have gotten the wrong plug gap from the parts store before.

You should check for power to the spark plugs:
Unplug the ignition coil wire from the distributor cap, hold it a half inch from the cylinder head and have someone crank the engine. See if a spark arcs across.

if there is no spark from the ignition coil wire then replacing the cap and wires probably won't help.

Since the car was sitting, did you replace the battery? Try adding booster cables connected to another vehicle and see if it starts up. If the battery is old and not supplying enough voltage, sometimes the coil won't even fire.

Also, try leaving the key in the ON position for a few minutes, then try starting it up. This will allow the ECU capacitors to charge up if they are going bad.

89's don't have many lights I'm thinking it's the CPS and possibly pinched or unplugged wiring if you pulled the body off and then put it back on If you've got fuel but not spark then I'd check the CPS for sure next.

I have a little '89 2.5 with 220,000 miles on it and it still sounds like a little sewing machine when it's running.